Japanese Patent Publication No. 2010-164234, for example, describes a known drain recovery device (condensate recovery device) that collects drain (condensate) generated by condensation of steam in a steam-using device and returns the collected drain to a boiler. Such a drain recovery device includes a recovery tank (drain tank) and a make-up water tank (mixing tank). The recovery tank collects drain generated in the steam-using device and stores the collected drain. The make-up water tank stores water generated by condensation of influent steam (flash steam) re-evaporated in the recovery tank or water supplied from another source. Water stored in the recovery tank and water stored in the make-up water tank are supplied to the boiler, and steam is generated by heating.
In such a drain recovery device, water in the recovery tank is mainly supplied to the boiler. Water in the make-up water tank is supplementarily supplied to the boiler when the water supply to the boiler runs short. Specifically, the drain recovery device controls the amount of drain supply from the recovery tank to the boiler so that the water level of the recovery tank does not decrease below a predetermined reference water level. When the water level decreases below the reference water level, for example, water is supplementarily supplied from the make-up water tank to the boiler.